1. Field of the Invention
The present invention relates to a photosensitive resin composition developable with water or a diluted alkali aqueous solution, and a photoresist ink for manufacturing printed wiring boards.
2. Disclosure of the Prior Art
In the past, photoresist inks developable with a diluted alkali aqueous solution have been used as inks for manufacturing printed wiring boards, screen printing stencils, color-filter pixels and color-filter protective films, or a photogravure ink. For example, such photoresist inks are disclosed in Japanese Patent Early Publications No. 5-224413 and No. 5-241340.
However, these photoresist inks contain various organic solvents such that they can be uniformly applied on substrates. The organic solvents are usually evaporated from the photoresist inks during a predrying step prior to a subsequent exposing step. Therefore, there are problems inherent in the use of the organic solvents such as a poor working condition, environmental pollution and the occurrence of a fire.
The present invention concerns a photosensitive resin composition developable with water or a diluted alkali aqueous solution, which is capable of improving the above problems. The photosensitive resin composition contains the following components (A) to (D). That is, the component (A) is a water-soluble photosensitive resin selected from the group consisting of a first resin obtained by introducing a styryl pyridinium group into a polyvinyl alcohol polymer, a second resin obtained by introducing a styryl quinolinium group into the polyvinyl alcohol polymer, and a third resin adding N-alkylol(meth)acrylamide to the polyvinyl alcohol polymer. The component (B) is a photosensitive prepolymer having a carboxyl group and at least two ethylenically unsaturated groups in molecule. The component (C) is a photopolymerization initiator. The component (D) is water.
It is preferred that the photosensitive resin composition further contains a photopolymerizable ethylenically-unsaturated monomer as the component (E).
It is particularly preferred to use the photosensitive resin composition of the present invention as a photoresist ink for manufacturing printed wiring boards.
These and still other objects and advantages will become apparent from the following detail descriptions of the preferred embodiments and examples of the invention.
In the present specification, xe2x80x9c(meth)acrylic-xe2x80x9d means xe2x80x9cacrylic-xe2x80x9d and xe2x80x9cmethacrylic-xe2x80x9d. For example, (meth)acrylic acid means acrylic acid and methacrylic acid. In addition, (meth)acrylamide means acrylamide and methacrylamide.
A photosensitive resin composition of the present invention comprises a water-soluble photosensitive resin (A), photosensitive prepolymer (B), photopolymerization initiator (C) and water (D).
The water-soluble photosensitive resin (A) is selected from the group consisting of a water-soluble photosensitive resin (A1) obtained by introducing a styryl pyridinium group or a styryl quinolinium group into a polyvinyl alcohol polymer, and a water-soluble photosensitive resin (A2) obtained by adding N-alkylol(meth)acrylamide to the polyvinyl alcohol polymer.
As the polyvinyl alcohol polymer used to prepare the photosensitive resin (A), for example, it is possible to use a polyvinyl alcohol obtained by complete saponification or a partial saponification of polyvinyl acetate, or a water-soluble polyvinyl alcohol derivative obtained by a reaction of xe2x80x94OH group or xe2x80x94OCOCH3 group of a completely-saponified or partially-saponified polyvinyl alcohol with an acid-anhydride containing compound, carboxy-group containing compound, epoxy-group containing compound, or an aldehyde-group containing compound. In addition, it is possible to use a vinyl alcohol copolymer having vinyl alcohol units, which is obtained by the complete saponification or the partial saponification of polyvinyl acetate. As the copolymer component of vinyl acetate, for example, it is possible to use (meth)acrylic acid, (meth)acrylamide, N-methylol(meth)acrylamide, styrene, ethylene, propylene, maleic anhydride, (meth)acrylonitrile, (meth)acrylic ester.
It is preferred that the polyvinyl alcohol polymer contains 60 mol % or more of the vinyl alcohol units within its polymerization unit. In particular, when using the polyvinyl alcohol polymer containing 80 mol % or more of the vinyl alcohol units, or the polyvinyl alcohol obtained by the complete saponification of polyvinyl acetate, there is an advantage that the photosensitive resin composition of the present invention is excellent in the water-solubility.
The photosensitive resin (A1) can be prepared by a conventional method disclosed in, for example, Japanese Patent Early Publication [KOKAI] No. 55-23163, No. 55-62905, or No. 56-11906.
Concretely, for example, the photosensitive resin (A1) can be obtained by adding a formyl styryl pyridinium salt or a formyl styryl quinolinium salt to the polyvinyl alcohol polymer according to an acetal reaction applying an alcoholic xe2x80x94OH group of the polyvinyl alcohol polymer.
The general formula (1) shows a typical structure of an introduced portion of the styryl pyridinium group in the photosensitive resin (A1). The general formula (2) shows a typical structure of an introduced portion of the styryl quinolinium group in the photosensitive resin (A 1). 
In these formulas (1) and (2), each of R1 and R2 is hydrogen atom, alkyl group, or aralkyl group, xe2x80x9cXxe2x88x92xe2x80x9d is a conjugate base of an acid, xe2x80x9cmxe2x80x9d is an integer of 1xcx9c6, and xe2x80x9cnxe2x80x9d is 0 or 1.
It is preferred that an introduction rate of the styryl pyridinium group or the styryl quinolinium group in the photosensitive resin (A1) is within a range of 0.3 to 20 mol %, and more preferably 0.5 to 10 mol %, per vinyl alcohol polymerization unit constructing the photosensitive resin (A1). In the range of 0.3 to 20 mol % of the introduction rate, the photosensitive resin (A1) is good in the water-solubility, and has a suitable photo-bridging capability.
The water-soluble photosensitive resin (A2) can be prepared by a conventional method disclosed in, for example, Japanese Patent Publication [KOKOKU] No. 49-5923, or Japanese Patent Early Publication [KOKAI] No. 62-267302.
Concretely, for example, the photosensitive resin (A2) can be obtained by an etherification reaction between a polyvinyl alcohol polymer and N-alkylol(meth)acrylamide in the presence of an acid catalyst such as inorganic acid or sulfonic acid derivative in a good solvent of the polyvinyl alcohol polymer such as water or a N-methyl pyrrolidone solution, or a suspension of a bad solvent of the polyvinyl alcohol polymer.
As the N-alkylol(meth)acrylamide, for example, it is possible to use N-methylol(meth)acrylamide, N-ethylol(meth)acrylamide, N-propylol(meth)acrylamide, or N-butylol(meth)acrylamide. The N-alkylol(meth)acrylamide can be one of these materials or can be a combination of two or more of these materials, if necessary.
It is preferred that an addition ratio of the N-alkylol(meth)acrylamide is within a range of 0.05 to 25 mol %, and more preferably 0.05 to 15 mol %, per vinyl alcohol polymerization unit constructing the photosensitive resin (A2). In the above range of the addition ratio, better water-solubility and photo-curability of the photosensitive resin (A2) can be obtained.
The photosensitive prepolymer (B) is a photosensitive prepolymer having a carboxyl group and at least two ethylenically unsaturated groups in molecule. The photosensitive prepolymer is characterized in that a plurality of groups having photopolymerizable ethylenically-unsaturated groups branch from a main chain of the prepolymer. Since the photosensitive prepolymer contains the carboxyl group, it can be swelled, dispersed or dissolved in a diluted alkali aqueous solution. However, when the photosensitive prepolymer is exposed in the presence of the photopolymerization initiator, the ethylenically unsaturated groups of the prepolymer molecules react each other to increase the molecular weight, so that the dispersing property or the solubility to the diluted alkali aqueous solution lowers.
Therefore, a film made of the photosensitive resin composition of the present invention containing the photosensitive prepolymer (B) can be swelled, dispersed or dissolved in the diluted alkali aqueous solution before the exposing step. However, after the film is cured by the exposing step according to photopolymerization, the dispersing property or the solubility to the diluted alkali aqueous solution lowers. Therefore, by applying a difference of the solubility of the photosensitive resin composition to the diluted alkali aqueous solution before and after the exposing step, it is possible to form a desired pattern of a cured film of the photosensitive resin composition. That is, the film of the photosensitive resin composition is selectively exposed, and then developed with the diluted alkali aqueous solution. The non-exposed region of the film is washed away to leave the exposed region of the film, so that the desired pattern of the cured film of the photosensitive resin composition is obtained.
The cured film of the photosensitive resin composition can be stripped and removed by the use of sodium periodate. Additionally, since the photosensitive resin composition of the present invention contains the photosensitive prepolymer (B) having the carboxyl group, the cured film can be stripped and removed by the use of an aqueous solution of alkali-metal hydroxide.
It is preferred that the photosensitive prepolymer (B) itself can form a film. In the present invention, since the photosensitive resin composition contains the photosensitive resin (A) and the photosensitive prepolymer (B), there is an advantage that a predried film of the photosensitive resin composition is substantially free from surface tackiness, so that contamination of a phototool artwork with the photosensitive resin composition can be prevented even when the artwork is directly put on the predried film.
It is preferred that an acid value of the photosensitive prepolymer (B) is within a range of 20 to 300 mgKOH/g, and more preferably 40 to 200 mgKOH/g. In this range of acid value, it is possible to shorten the developing time when developing the photosensitive resin composition with the diluted alkali aqueous solution. In addition, since the resistance to diluted alkali aqueous solution of the cured film of the photosensitive resin composition adequately lowers, a better pattern of the cured film can be easily formed.
It is also preferred that a weight-average molecular weight of the photosensitive prepolymer (B) is within a range of 2000 to 250000, and more preferably 4000 to 100000. In the above range of weight-average molecular weight, it is possible to stably obtain a sufficient photosensitivity of the photosensitive resin composition. In addition, when the weight-average molecular weight is less than 2000, there is a possibility that the surface tackiness of the predried film occurs. On the other hand, as the weight-average molecular weight exceeds 250000, there is a tendency of lowering the developing property.
The carboxyl group of the prepolymer (B) may be neutralized by an organic basic compound such as alkanol amine, alkali-metal hydroxide, or an inorganic basic compound such as ammonia.
As the prepolymer (B), for example, it is possible to use a photosensitive prepolymer (B 1) obtained by adding an ethylenically unsaturated monocarboxylic acid and an unsaturated or saturated polybasic acid anhydride to a polyfunctional epoxy compound having at least two epoxy groups.
As the polyfunctional epoxy compound of the prepolymer (B 1), for example, it is possible to use a phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, bisphenol A-type epoxy resin, bisphenol A-novolac-type epoxy resin, bisphenol F-type epoxy resin, N-glycidyl-type epoxy resin, alicyclic-type epoxy resin (e.g., xe2x80x9cEHPE-3150xe2x80x9d manufactured by Daicel Chemical Industries, Ltd.), tris (hydroxyphenyl) methane-based polyfunctional epoxy resin (e.g., xe2x80x9cEPPN-502Hxe2x80x9d manufactured by NIPPON KAYAKU Co., LTD. or xe2x80x9cTACTIX-742xe2x80x9d and xe2x80x9cXD-905xe2x80x9d manufactured by DOW CHEMICAL), dicyclopentadiene-phenol-type epoxy resin, naphthalene-type epoxy resin. As the ethytenically unsaturated monocarboxylic acid, for example, it is possible to use (meth)acrylic acid.
As the unsaturated or saturated polybasic acid anhydride of the prepolymer (B1), for example, it is possible to use a dibasic acid anhydride such as succinic anhydride, methyl succinic anhydride, maleic anhydride, citraconic anhydride, glutaric anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, methyl nadic acid anhydride, hexahydrophthalic anhydride, and methyl hexahydrophthalic anhydride, or a polybasic acid anhydride such as trimellitic acid anhydride, pyromellitic acid anhydride, benzophenone tetracarboxylic anhydride and methyl cyclohexene tetracarboxylic anhydride.
In addition, as the prepolymer (B), it is possible to use a photosensitive prepolymer (B2) obtained by a reaction of a compound having a photoreactive ethylenically unsaturated group and a hydroxyl group in molecule with a copolymer of an unsaturated polybasic acid anhydride such as maleic anhydride and an aromatic hydrocarbon having a vinyl group such as styrene or vinyl alkyl ether.
As the compound of the prepolymer (B2), for example, it is possible to use 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, diethylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate, or dibutylene glycol mono(meth)acrylate.
Moreover, as the prepolymer (B), for example, it is possible to use a photosensitive prepolymer (B3) obtained by a reaction of an ethylenically unsaturated compound having a single epoxy group with a copolymer of a first ethylenically unsaturated monomer having no carboxyl group and a second ethylenically unsaturated monomer having the carboxyl group.
As the first ethylenically unsaturated monomer, for example, it is possible to use a straight-chained or branch-chained alkyl(meth)acrylate, alicyclic(meth)acrylate (an unsaturated bonding may be included in its ring.), ethylene glycol ester-type (meth)acrylate such as hydroxyethyl(meth)acrylate, methoxyethyl(meth)acrylate, propylene glycol-type (meth)acrylate, glycerol mono(meth)acrylate, aromatic-type (meth)acrylate such as benzyl(meth)acrylate, acrylamide-type compound such as (meth)acrylamide, N-methyl(meth)acrylamide, N-propyl(meth)acrylamide and diacetone(meth)acrylamide, vinyl pyrrolidone, acrylonitrile, vinyl acetate, styrene, xcex1-methyl styrene, or vinyl ether.
As the second ethylenically unsaturated monomer, for example, it is possible to use (meth)acrylic acid, maleic acid, crotonic acid, or itaconic acid.
As the ethylenically unsaturated compound having the single epoxy group of the prepolymer (B3), for example, it is possible to use a glycidyl(meth)acrylate such as glycidyl(meth)acrylate and 2-methylglycidyl(meth)acrylate, or an epoxy cyclohexyl derivative of a (meth)acrylic acid such as (3,4-epoxy cyclohexyl)methyl(meth) acrylate.
As the prepolymer (B), for example, it is also possible to use a photosensitive prepolymer (B4) obtained by a reaction of a polymer or a copolymer containing an ethylenically unsaturated monomer having an epoxy group as polymerization unit with an unsaturated monocarboxylic acid and a saturated or unsaturated polybasic acid anhydride. The prepolymer (B4) can be prepared by conventional methods.
As the ethylenically unsaturated monomer having the epoxy group of the prepolymer (B4), for example, it is possible to use the ethylenically unsaturated compound having the single epoxy group of the prepolymer (B3).
When using the copolymer containing the ethylenically unsaturated monomer, it is possible to use an unsaturated monomer polymerizable with the ethylenically unsaturated monomer having the epoxy group. For example, the first ethylenically unsaturated monomer of the prepolymer (B3) may be used as the unsaturated monomer.
As the unsaturated monocarboxylic acid and the saturated or unsaturated polybasic acid anhydride of the prepolymer (B4), for example, it is possible to use those of the prepolymer (B1).
In addition, as the prepolymer (B), for example, it is possible to use a photosensitive prepolymer (B5) obtained by a reaction of parts of carboxyl groups in a cellulose derivative having carboxyl groups with a compound having an epoxy group and at least one ethylenically unsaturated group.
For example, the prepolymer (B5) can be prepared by the following method. That is, the compound having the epoxy group and at least one ethylenically unsaturated group is added to a hydrophilic solvent solution of the cellulose derivative in the presence of a polymerization inhibitor and a catalyst. The resultant is agitated and mixed to obtain a mixture. The mixture is kept at a reaction temperature of 60 to 150xc2x0 C., and more preferably 80 to 120xc2x0 C. to obtain the prepolymer (B5). As the polymerization inhibitor, it is possible to use hydroquinone or hydroquinone monomethyl ether. As the catalyst, it is possible to use a tertiary amine such as benzyl dimethyl amine and triethyl amine, a quaternary ammonium salt such as trimethyl benzyl ammonium chloride and methyl triethyl ammonium chloride, or triphenyl stibine.
As the cellulose derivative of the prepolymer (B5), for example, it is possible to use hydroxypropyl methylcellulose phthalate, hydroxypropyl methylcellulose acetate succinate, cellulose acetate hexahydrophthalate, hydroxypropyl methylcellulose acetate phthalate, or hydroxypropyl methylcellulose hexahydrophthalate.
As the compound having the epoxy group and at least one ethylenically unsaturated group of the prepolymer (B5), for example, it is possible to use a glycidyl(meth)acrylate such as glycidyl(meth) acrylate and 2-methyl glycidyl(meth)acrylate, or an epoxy cyclohexyl derivative of a (meth)acrylic acid such as (3,4-epoxy cyclohexyl) methyl(meth)acrylate.
By the way, when all of the carboxyl groups in the cellulose derivative reacts with epoxy groups, the prepolymer (B5) of the reaction product becomes to be insoluble to the diluted alkali aqueous solution. Therefore, an amount used of the compound having the epoxy group and at least one ethylenically unsaturated group should be determined such that parts of carboxyl groups of the cellulose derivative remain in the prepolymer (B5).
In addition, as the prepolymer (B), for example, it is possible to use a photosensitive prepolymer (B6) obtained by a reaction of a compound having a single epoxy group and at least one ethylenically unsaturated group and a saturated or unsaturated polybasic acid anhydride with a cellulose derivative having carboxyl groups.
For example, the prepolymer (B6) can be prepared by the following method. That is, a reaction product is obtained by a reaction of all or parts of the carboxyl groups of the cellulose derivative with the compound having the single epoxy group and at least one ethylenically unsaturated group. Then, the saturated or unsaturated polybasic acid anhydride is added to the reaction product to obtain the prepolymer (B6). As a method of preparing the reaction product, it is possible to use the same method explained for the prepolymer (B5). The addition reaction can be performed according to conventional methods.
As the cellulose derivative and the compound having the epoxy group and at least one ethylenically unsaturated group of the prepolymer (B6), for example, it is possible to use those of the prepolymer (B5). As the saturated or unsaturated polybasic acid anhydride of the prepolymer (B6), for example, it is possible to use those of the prepolymer (B 1).
As the photopolymerization initiator (C), for example, it is possible to use benzoin, alkyl ether of benzoin such as benzoin methyl ether, benzoin ethyl ether and benzoin isopropyl ether, acetophenone such as acetophenone, 2,2-dimethoxy-2-phenyl acetophenone, 2,2-diethoxy-2-phenyl acetophenone, 1,1-dichioro acetophenone, 1-hydroxy cyclohexyl phenyl ketone, and 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl) ketone, anthraquinone such as 2-methyl anthraquinone and 2-amyl anthraquinone, thioxanthone such as 2,4-dimethyl thioxanthone, 2,4-diethy thioxanthone, 2-chloro thioxanthone, 2,4-diisopropyl thioxanthone and 1-chloro-4-propoxy thioxanthone, ketal such as acetophenone dimethyl ketal and benzyl dimethyl ketal, xanthone, benzophenone such as 3,3-dimethyl-4-methoxy benzophenone, 3,3xe2x80x2,4, 4xe2x80x2-tetra-(tert-butyl peroxyl carbonyl) benzophenone and 4-benzoyl-4xe2x80x2-methyl diphenyl sulfido, nitrogen-containing compound such as 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propane-1-on, 2benzoyl-2-dimethyl amino-1(4-morpholino phenyl)-butanone-1, and 4,-4xe2x80x2-bis-diethyl amino benzophenone, or 2,4,6-trimethyl benzoyl diphenyl phosphine oxide. The photopolymerization initiator can be one of these materials, or can be a combination of two or more of these materials, if necessary.
The photopolymerization initiator (C) may be used together with a conventional photopolymerization enhancer or sensitizer such as a benzoic acid, and a tertiary amine, e.g., p-dimethyl amino benzoic acid ethyl ester, p-dimethyl amino benzoic acid isoamyl ester, and 2-dimethyl amino ethyl benzoate.
As a first optional component, the photosensitive resin composition of the present invention can contain a photopolymerizable ethylenically unsaturated monomer (E). As the monomer (E), for example, it is possible to use trimethylol propane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butanediol diacrylate, 1,6-hexane diol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 2,2-bis[4-((meth)acryloxy ethoxy) phenyl]propane, 2,2-bis[4-((meth)acryloxy diethoxy) phenyl]propane, 2-hydroxy-1,3-di(meth)acryloxy propane, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, phenoxy ethyl(meth)acrylate, phenoxy diethylene glycol(meth)acrylate, methoxy diethylene glycol(meth)acrylate, tetrahydro furfuryl(meth)acrylate, dicyclopentenyl hydroxy ethyl(meth)acrylate, 1-methoxy dodecadienyl(meth)acrylate, xcex2-(meth)acryloyl hydroxy ethyl hydrogen phthalate, xcex2-(meth)acryloyl hydroxy ethyl hydrogen succinate, 3-chloro-2-hydroxy propyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, stearyl(meth)acrylate, bisphenol A-diepoxy acrylic acid adduct, (meth)acrylamide, N-methoxy methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acryloyl morpholine, N-methylol(meth) acrylamide, hydroxy propyl(meth)acrylate, polyethylene glycol di (meth)acrylate, methylene bis(meth)acrylamide, 2-hydroxy ethyl (meth)acrylate,2,2-bis[4-methacryloyl hydroxy polyethoxy phenyl]propane. The monomer (E) can be one of these materials or can be a combination of two or more of these materials, if necessary.
As a second optional component, the photosensitive resin composition of the present invention can contain an organic solvent. An amount used of the organic solvent should be determined such that the problems inherent in the use of the organic solvent are ignorable. For example, as the organic solvent, it is possible to use an alcohol such as ethanol, propanol, 2-propanol, butanol, 2-butanol, hexanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, trimethylol propane, neopentyl glycol, glycerin, 1,2,4-butanetriol, 1,2-butanediol, 1,4-butanediol and diacetone alcohol, ethylene glycol alkyl ether such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether, polyethylene glycol alkyl ether such as diethylene glycol monomethyl ether, diethylene glycol monocthyl ether and triethylene glycol monomethyl ether, propylene glycol alkyl ether such as propylene glycol monomethyl ether, polypropylene glycol alkyl ether such as dipropylene glycol monomethyl ether, acetic ester such as ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, glycerin monoacetate and glycerin diacetate, lactic ester such as lactic ethyl and lactic butyl, dialkyl glycol ether such as diethylene glycol diethyl ether, ketone such as methyl ethyl ketone, cyclohexanone and isophorone, aromatic hydrocarbon such as toluene and xylene, oil and aromatic-type mixed solvent such as xe2x80x9cSWASOL SERIESxe2x80x9d (manufactured by Maruzen Petrochemical Co., Ltd.) and xe2x80x9cSOLVESSO SERIESxe2x80x9d (manufactured by EXXON CHEMICAL COMPANY), n-hexane, cyclohexane, or tetrahydrofuran. The organic solvent can be one of these materials, or can be a combination of two or more of these materials, if necessary.
The photosensitive resin composition of the present invention may also contain a leveling agent such as a fluorine surface active agent, silicone and a (meth)acrylate copolymer, a thixotropic agent such as AEROSIL, a polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether, pyrogallol, tert-butyl catechol and phenothiazine, antihalation agent, flame retardant, plating-resistance improving agent, defoamer, anti-oxidant, pigment wetting agent, organic or inorganic pigment and dye, additives such as synthetic rubber powder and natural rubber powder, high molecular dispersing agent or surface-active agent for improving the dispersion stability.
It is preferred to prepare the photosensitive resin composition of the present invention according to the following compounding amounts of the water-soluble photosensitive resin (A), photosensitive prepolymer (B), photopolymerization initiator (C) and water (D).
That is, it is preferred that the compounding amount of the water-soluble photosensitive resin (A) is 0.1 to 50 wt %, and more preferably 1 to 30 wt % with respect to the total amount of all components of the photosensitive resin composition except for water (D) and the organic solvent as the second optional component. In the above range, there are advantages that (1) the photosensitive resin composition is excellent in the water-solubility; (2) a cured film of the photosensitive resin composition exhibits good water resistance; and (3) a peeling of the cured film is hardly generated at the time of the formation of the cured film. In particular, when the compounding amount is 0.5 to 50 wt %, the photosensitive resin composition can be easily developed with water.
It is preferred that the compounding amount of the photosensitive prepolymer (B) is 30 wt % or more with respect to the total amount of all components of the photosensitive resin composition except for water (D) and the organic solvent as the second optional component. In the above range, there is an advantage that a predried film of the photosensitive resin composition is almost free from the surface tackiness.
It is preferred that the compounding amount of the photopolymerization initiator (C) is within a range of 0.1 to 20 wt % with respect to the total amount of all components of the photosensitive resin composition except for water (D) and the organic solvent as the second optional component. In the above range, there is an advantage that the photosensitive resin composition is excellent in the photo-curability.
It is preferred that the compounding amount of water (D) is within a range of 10 to 97 wt % with respect to the total amount of all components of the photosensitive resin composition. In the above range, there is an advantage that the fluidity of the photosensitive resin composition is suitable to uniformly apply the resin composition on substrates. When the photosensitive resin composition contains the ethylenically unsaturated monomer (E), it is preferred that the compounding amount of the monomer (E) is 75 wt % or less with respect to the total amount of all components of the photosensitive resin composition except for water (D) and the organic solvent as the second optional component. The monomer (E) is useful to more improve the photoreactivity of the photosensitive resin composition. When the compounding amount is more than 75 wt %, there is a possibility that the surface tackiness of the predried film of the photosensitive resin composition comes into problem.
There is no limitation as to a method of preparing the photosensitive resin composition of the present invention. For example, the components (A) to (C) and the other optional components may be dissolved, emulsified, and dispersed in water (D) or a mixture of water and an aqueous organic solvent to obtain the photosensitive resin composition. Alternatively, an aqueous solution of the component (A) may be added to the components (B) and (C) and the other optional components, and then mixed to obtain the photosensitive resin composition. In these methods, it is preferred to use an agitator or a muller such as homomixer, pipeline homomixer, bead mill, roll mill and ball mill.
Next, a method of forming a required pattern on a substrate with the use of the photosensitive resin composition of the present invention is explained as an example.
 less than Applying Step greater than 
First, the photosensitive resin composition can be applied on a substrate by a dipping method, spray method, spin-coating method, roll method. A copper clad laminate used to manufacture printed wiring boards may be used as the substrate.
 less than Predrying Step greater than 
The photosensitive resin composition on the substrate can be dried by a hot-air drying method, electromagnetic induction heating, hot-pressing, or a far-infrared drying method to obtain a predried film.
 less than Exposing Step greater than 
After a mask having a required pattern such as a phototool artwork is directly or indirectly put on the predried film, ultraviolet can be radiated to the predried film through the mask by using a tungsten lamp, chemical lamp, low-pressure mercury lamp, medium-pressure mercury lamp, high-pressure mercury lamp, extra-high-pressure mercury lamp, xenon lamp or a metalhalide lamp. Alternatively, it is preferred to adopt a laser patterning method using a helium-cadmium laser, argon laser or a YAG laser.
 less than Developing Step greater than 
After the exposing step, the predried film can be developed with water or a diluted alkali aqueous solution, so that the non-exposed region of the predried film is washed away to leave the exposed region of the predried film on the substrate as a resist pattern. When developing with the diluted alkali aqueous solution, it is preferred to use an aqueous solution of an alkali hydroxide such as sodium hydroxide, potassium hydroxide and lithium hydroxide, or an alkali carbonate such as sodium carbonate and potassium carbonate.
 less than Etching or Plating Step greater than 
The etching or plating step can be performed to the substrate surface exposed through the resist pattern by conventional methods. When performing the etching step, it is preferred to select an etching agent in accordance with a material of a conductive layer of the substrate. For example, an acid etching solution such as copper (II) chloride, or an ammonia etching solution may be used. When performing the plating step, it is possible to perform a copper plating such as a copper-sulfate plating and a copper pyrophosphate plating, solder plating such as a high throw solder plating, nickel plating such as a nickel sulfamate plating, or a gold plating such as a soft gold plating and a hard gold plating.
 less than Removing Step of Resist Pattern greater than 
When it is required to strip and remove the resist pattern from the substrate, the resist pattern can be readily stripped and removed with the use of sodium periodate or sodium hypochlorite. Alternatively, it is possible to remove the resist film from the substrate with the use of a stronger alkali aqueous solution than the alkali aqueous solution used at the developing step.
Consequently, the photosensitive resin composition of the present invention can provide the following advantages.
(1) Since the photosensitive resin composition does not essentially contain the organic solvent, it is possible to prevent the occurrence of the problems inherent in the use of the organic solvent.
(2) A predried film of the photosensitive resin composition can be developed with water or a diluted alkali aqueous solution.
(3) A film of the photosensitive resin composition cured by the photopolymerization reaction is excellent in film hardness, resistance to etching solution, resistance to plating solution, and thermal resistance. In addition, the cured film has good adhesion with the substrate.
(4) The cured film of the photosensitive resin composition can be removed from the substrate with the use of sodium periodate or an aqueous solution of an alkali-metal hydroxide.
Therefore, the photosensitive resin composition of the present invention will be preferably used as a photoresist ink for manufacturing printed wiring boards such as an etching resist ink, plating resist ink, solder resist ink and marking ink, photoresist ink for photogravure, photosensitive composition for manufacturing screen printing stencils, ink for manufacturing color-filter pixels, or an ink for manufacturing color-filter protective films.